In a system, data may be transmitted in either encrypted or unencrypted form, depending on the conditions, type of data, devices involved, and other factors. In one example, multimedia content, including video data for display, may be received in an encrypted form or unencrypted form depending on the security requirements for the particular data and the types of devices that are involved. Data may include HDMI™ (High-Definition Multimedia Interface) data, where HDMI provides an audio/video interface for transmitting uncompressed digital data. In one example, HDCP™ (High-bandwidth Digital Content Protection) is utilized for digital content protection, providing for encryption of content transmitted over digital interfaces, including HDMI. Content transmitted via an HDMI interface may or may not be encrypted utilizing HDCP, depending on the circumstances.
Encryption technologies, such as HDCP, may not provide a continuous mechanism for detecting an actively-encrypted stream at the receiver end of the link. In a conventional system, an additional process to determine whether a stream of data is encrypted beyond information such as, for example, HDCP notifications sent once per frame, may be required. A system receiving video or audio-video data (which may be referred to as a “sink”) from a transmitting system (which may be referred to as a “source”) may provide for measurement of data regarding encryption to determine encryption of a data stream. For example, a system receiving video or audio-video data may provide for detection of an OESS (Original Encryption Status Signaling) or EESS (Enhanced Encryption Status Signaling) signal, with such data being provided once prior to transmission of each frame. EESS and OESS are protocols for signaling whether encryption is enabled or disabled for a frame, where EESS protocol is used with the HDMI protocol (and is an optional feature in the DVI™ (Digital Visual Interface) protocol), and where OESS is used with the DVI protocol.
However, the detection of encryption data signaling in a blanking interval generally requires that a system monitor each channel for such signaling regarding encryption. If the signaling is not detected, a conventional system will determine that data is not encrypted. However, if the lack of detection of encryption is due to an error, the system will attempt to utilize data as unencrypted data, thus resulting in errors and delay in processing. A loss of encryption detection or resulting loss of synchronization for encryption may result in to data errors when encryption resumes, even if, for example, encryption is halted temporarily by the source. The loss of synchronization may result in an inaccurate frame index count for an input port, which may result in a failing link integrity check, requiring re-authentication, or leading to an undetected link integrity problem thereby, causing ongoing errors in decryption and a poor quality picture on the display.